Hydraulic apparatus for applying tension to cables



March 5, 1968 F. M. sTlNToN 3,371,909

HYDRAULIC APPARATUS FOR APPLYING TENSION TO CABLES Filed Nov. 23, 1966 5 Sheets-Sheet l FRYEmcK M. STlNToN Mm/mwawwg www.

9 ATT'Ys F. M. STINTON March 5, 1968 HYDRAULIC APPARATUS FOR APPLYING TENSION T0 CABLES 5 Sheets-Sheei 2 Filed Nov. 25, 1966 INVENTQR: FREDERICK M. STINTON ATT'YS March 5, 1968 F. M. sTlNTON HYDRAULIC APPARATUS FOR APPLYING TENSION TO CABLES 5 Sheets-Sheet INVENTOR: FREDERICK Nl. STINTON .f BY

ATT' YS Filed Nov. 23, y 1966 United States Patent Office 3,371,909 HYDRAULIC APPARATUS FOR APPLYING TENSION TO CABLES Frederick M. Stinton, Glen Ellyn, Ill., assignor, by mesne assignments, to F. M. Stinton, Inc., Hinsdale, Ill., a corporation of Illinois Filed Nov. 23, 1966, Ser. No. 596,579 Claims. (Cl. 254-29) ABSTRACT OF THE DISCLOSURE First and second hydraulic jacks are mounted within a rigid, unitary frame for applying a prestressing force to collinear cables embedded in concrete and extending into a common, central pocket in the concrete. Each of the jacks has a fixed component attached to the frame and a movable component adapted for opposing motion longitudinally of the cables that are to be tensioned. Each of the movable components is provided with means for engaging and holding its associated cable; and when the jacks are expanded, the movable components are forced in opposing motion thereby pulling the cables together and applying tension to each cable.

This invention relates to apparatus for applying tensional force to cables embedded in concrete for prestressing the concrete. More particularly, this invention relates to hydraulic apparatus for applying tensional force to collinear portions of separate cables in prestressing concrete.

Prior art devices for applying tension to cables for prestressing concrete include the use of devices such as scissors, jacks and the like, which are cumbersome in transportation and awkward in field use. Hydraulic jacks have been used in this application, but heretofore such applications have also been cumbersome and difficult to set up in the field. In addition, prior art hydraulic jacks have been designed for use in situations in which the tensioning cables extend out of a terminating edge of the concrete so that there is little or no restriction on the size of the equipment in the direction of the extended cable.

One object of the presentinvention is to provide for hydraulic jack apparatus for prestressing concrete which is easily transportable, convenient for use in the field, and economical to construct.

Another object of the present invention is to provide a prestressing hydraulic asesmbly for use in applying tension to cables which extend collinearly into a preformed pocket in a concrete slab wherein the space for access to the fastening heads of the cables is limited by an adjacent fastening head of the associated collinear cable.

Still another object of the present invention is to provide a hydraulic assembly for applying tension to cables for prestressing concrete wherein the cables extend collinearly into a preformed pocket in the concrete and the assembly may be adapted to apply additional tension in one of the cables while maintaining a substantially constant tension in the other cable.

It is noted that the embodiment hereafter illustrated is particularly adapted for use in my new method of prestressing concrete described in co-pending application, Method for Central Prestressing of Concrete, but it is not intended that the invention be limited to use with that method since it is readily adaptable to use with more common and presently-known prestressing methods.

Further objects and advantages of the present invention will be clear from the following description accompanied by the attached drawing, in which- FIG. 1 is a partially cut away isometric view of ap- 3,371,909 Patented Mar. 5, 1968 paratus according to the present invention shown in a typical use with tension cables;

FIG. 2 is a close-up view of a portion of FIG. 1 showing the shoes of the jack assembly adapted to lit into a preferred cable fastening head;

FIG. 3 is a top view of lthe apparatus of FIG. l;

FIG. 4 is a side section taken along the line 4 4 of FIG. 3 in the direction of the arrows;

FIG. 5 shows the same view as FIG. -4 and further indicates an alternate position of the locking subassembly;

FIG. 6 is a side View of a typical method of laying the tension cables suitable for use with the apparatus of FIG. l;

FIG. 7 is a section view through the lines 7-7 of FIG. 4 in the direction of the arrows;

FIG. 8 is a close-up view of the stool of FIG. 6;

FIG. 9 is a section view taken through the line 9-9 of FIG. 8 in the direction of the arrows; and

FIG. l0 is a side view taken from the line 10-10 of FIG. 8 in the direction of the arrows.

Referring then to FIG. l, reference numeral 10 indicates generally a slab of hardened concrete to be prestressed. A tensioning cable 11 is shown wrapped in a paper wrapping, as is conventional. The cable 11 is embedded in concrete 10. The cable 11, as indicated in my co-pending application, is preferably formed by wrapping a continuous wire around a first fastening head 12, and a complementary fastening head (not shown). The Wrapping paper 11a forms a channel through which the cable 11 may be pulled. A lubricant is provided between the cable 11 and its wrapping paper 11a.

FIG. l illustrates both a completed assembly of cables permanently fastened together and a pair of cables undergoing tension with like reference numerals indicating identical elements of the two showings. The upper lefthand portion of FIG. 1 shows a completed assembly of two collinear cables, 11 and 11b which have been stressed to the desired degree and fastened permanently together by means of a bolt 14 and nuts 15. It will be noticed that the tWo tension cables 11 and 11b are brought out into a pocket, preformed in and extending completely through the concrete slab 10, and designated generally by reference numeral 13. The bolt 14 is fitted through apertures provided in the fastening blocks 12 and 12a, and fastened thereto by means of the nuts 15.

Centered in the lower right-hand portion and extending diagonally across FIG. 1 is a preferred embodiment of the prestressing apparatus. A frame, generally designated as 20, comprising two side guide rails 21 and 22 and back plates 23a and 23b is elongated in the direction of the collinear cables 11 and 11b, the frame 20 resting on the top of the concrete slab 10. The guide rails 21 and 22 are each attached, as by welding, at their ends to back plates 23a and 23b.

A first hydraulic jack 24 is located above and generally in the vertical plane containing tensioning cable 11. Hydraulic jack 24 is conventional and comprises a piston rod and cylinder 24a and a casing 24b, coaxial with the piston rod 24a and moveable along the axis thereof, as is -well known in the art. The end of piston rod 24a is fixed to back plate 23a, as at 25. When the jack 24 is expanded under high pressure from a source not shown, the piston rod 25 remains stationary and is forced against back plate 23a; and the casing 24h moves generally parallel with cable 11 toward the center tof pocket 13.

The casing 24h of hydraulic jack 24 is constrained to linear movement by means of two guide plates 26 fixed to the casing 24a and slideably engaging guide rails 21 and 22 as seen more clearly in FIG. 7, Guide plates 26 have a generally square shape and fit into the inner U-shaped contours of guide rails 21 and 22, formed by lips extending inwardly above and below guide plates 26. For `reasons mentioned below, it will be noted that the lower lips of guide rails 21 and 22 do not extend outwardly of the sides of the rails, but the upper lips do, as illustrated.

A second hydraulic jack 27 is axially aligned with, and opposite hydraulic jack 24. A piston rod 27a of jack 27 is fixed to and bears against back plate 23h. Casing 27h of cylinder 27 is fitted through guide plates 28 similar to guide plates 26; and the sides of guide plates 23 similarly engage the inner U-shape of guide rails 21 and 22 and are constrained thereby from any movement in the plane of the page of FIG. 7.

To each of the cylinder casings 24a and 27a is attached a shoe, designated respectively as 30 and 31, which extends below thc upper surface of concrete slab 1f) into pocket 13. FIG. 2 more clearly illustrates the details of shoe 31 and it is to be noted that shoe 30 is similarly constructed. Shoe 31 is attached, as by welding, to the movable end of casing 27b of hydraulic jack 27 and comprises two vertical side plates, designated respectively as 31a and 31b. Each of side plates 31a and 31h contains a web portion shown at 31C of FIG. 2, which is welded to the lower surface of casing 27b to resist bending moments of the side plates 31b. Side plates 31a and 31h are held apart by cross bars indicated at 31d so that a unitary rigid structure is formed. Each of the side plates 31a and 31b extends down into the pocket 13 formed in cement slab below the center line of the extended tension cables 11 and 11b. Each side plate 31a and 31b is further fitted with a key, indicated respectively at 32 and 33, which extends inwardly of the side plates 31a and 31h, and is adapted to fit into a corresponding receiving portion in the fastening head 12, as indicated in the pulled-apart view of FIG. 2. Keys 32 and 33 of shoe 31, which, as mentioned, are received by complementary shaped passages in fastening head 12, prevent rotary movement of tension cable 10. It will be noted that various other shoes may be adapted for use with different fastening heads, but for purposes of illustration, I have indicated the fastening head in my copending application.

FIG. 3, which is a top plan view of the prestressing apparatus of FIG. l, indicates that the tensional force is transmitted through shoes and 31 from the movable casings 24a and 27b respectively of expanded jacks 24 and 27. A coupling is provided in each of the casings 24b and 27b of the hydraulic cylinders 24 and 27 for the introduction of highly pressurized fluid as at 35a and 35b of FIG. 1.

As mentioned above, the illustrated prestressing apparatus has been designed for use with the method of my copending application in which two collinear tension cables are brought into tension against each other and then permanently fastened together to impart a predetermined tension. However, it is sometimes desirable, as when uneven tensional forces are noted in different cables, to maintain the force application of one of the cables constant and thereafter continue to increase the tension in the other. It is therefore considered an important feature of the present invention that some means is provided for employing the same prestressing apparatus when it is desirable to exert additional tensional force on only one of the tension cables.

For this purpose, referring particularly to FIGS. 1, 4 and 5, the prestressing apparatus has been fitted with four rods designated respectively as 36, 37, 38, and 39 (see FIG. 1) which extend longitudinally of the frame 20 and are fastened at opposite ends to the back plates 23a and 23b. A first locking block 40 has two apertures through which rods 36 and 37 fit to allow the block 40 to slide along the rods 36 and 3'7. A second locking block 41 is similarly adapted to slide along the rods 38 and 39. Each of the locking blocks 40 and 41 is independently movable along its respective set of rods, and each may be fastened rigidly to its rods by way of bolts, indicated at 42, threaded onto the center portions of rods 36, 37, 38, and 39.

FIG. 4 shows locking block 41 situated near the center of the apparatus, in which case it is not being used. However, if it were desirable to place additional stress, for instance, on cable 11b of FIG. 4, and at the same time to retain constant tension on the cable 11, then locking blocks 40 and 41 are moved to the extreme right of the pocket 13 so that the right-hand faces of locking blocks 40 and 41 bear against the right side 44 of pocket 13, as shown in FIG. 5. The pressure in hydraulic jack 24 is maintained constant and hydraulic jack 27 is expanded to apply additional tension to cable 11b. An opposing force will be transmitted through the apparatus frame 20 to the right-hand face of locking blocks 40 and 41 bearing against the left-hand face 44 of pocket 13 without additional tension being applied to cable 11 since frame 20 is constrained from movement in the right hand.

It will be further noted that the rods 36, 37, 38, and 39 are threaded at least throughout a substantial portion of their midsection to allow for maximum flexibility in placement of the locking blocks 40 and 41, but that the locking blocks 40 and 41 are preferably not threaded on the rods.

FIGS. 6-10 illustrate a typical method of prestressing concrete in which the described apparatus is suited for use. The concrete slab 10 rests on concrete blocks designated as 5f). The tension cables 11 and 11b extend collinearly into a pocket 13. Prior to pouring the concrete slab (which is monolithically poured) the tension cables 11 and 11b are set up on forms and supported by fourlegged stools 51 which are designed to place cables at varying heights above a horizontal plane, as can be seen from the drawing. The construction of stools 51 is more clearly illustrated in FIGS. 8-9 as having a saddle-shaped top for supporting the tension cable.

FIG. l0 illustrates the twopieced Wood form 52 used to sealably engage the tension cable and form one end of pocket 13 in the concrete slab 10. The upper and lower portions 52a and 52h of the form 52 have semi-circular cutouts which form the seal around the tension cable.

FIG. 7 shows a guide plate 26 fastened to the casing 24a of hydraulic jack 24 by means of a cylindrical jacket 63. The lower lips of guide rails 21 and 22 do not extend outwardly so that locking blocks 40 and 41 may fit closer to the vertical walls of the guide rails 21 and 22 (which are seen as having a J-shaped cross-section) for more compact construction.

It will be obvious that my invention is susceptible of modifications and substitution of equivalent structures well within the skill of the art and adapted to practice the principle of the invention. It is intended that any such equivalent structures and modifications falling Within the spirit and scope of the appended claims be covered.

What is claimed is:

1. Apparatus for use in applying tension force to first and second tension cables embedded in concrete for prestressing the same, each of said cables extending out of facing surfaces defining a pocket in said concrete comprising:

a unitary, rigid frame adapted for placement on said concrete above said pocket;

first hydraulic jacking means having a first fixed component attached to said frame and a second component linearly movable with respect to said fixed component longitudinally of said first cable and including means mounted on said movable component for engaging and holding said first cable;

second hydraulic jacking means independently operable from said first jacking means and having a first fixed component attached to said frame and a second component linearly movable with respect to said fixed component of said second jacking means in opposing direction to said movable component of said first jacking means and longitudinally of said second cable, and including means mounted on said movable component of said second jacking means for engaging and holding said second cable;

whereby said movable components of said first and second jacking means are forced together longitudinally of said first and second cables when said first and second jacking means are expanded thereby applying tension to said cables by forcing said cables toward each other.

2. The apparatus of claim 1 further comprising:

first and second locking blocks slidably carried by said frame on either side of said first and second jacking means and adapted to slide longitudinally of said cables, each of said locking blocks extending out and movable longitudinally of said frame for engaging either of said concrete surfaces;

means carried by said frame for securing said locking blocks in a predetermined position;

whereby when tension has been applied to said cables,

said locking blocks may be secured in engagement with the concrete surface out of which one tension cable extends, and the jacking means stressing that cable may be independently expanded to increase the tensional force therein while maintaining the other cable under constant tension.

3. The apparatus of claim 1 wherein said frame is an elongated, rigid rectangular structure comprising first and second back plates in a plane generally perpendicular to the motion of said movable components of said first and second jacking means and side walls defining guide rails fastened to said back plates; and said apparatus further includes first and second guide plate means rigidly attached respectively to the movable components of said first and second jacking means, said guide plate means engaging said guide rails and being constrained thereby to guide said movable components in linear movement longitudinally of said cables.

4. The apparatus of claim 1 wherein said cables are each provided with a fastening head and wherein said means for engaging and holding said first and second cables include a first shoe mounted on the movable cornponent of said first jacking means and a second shoe mounted on the m-ovable component of said second jacking means, each of said shoes comprising:

first and second side plates facing each other disposed in vertical planes extending longitudinally of said cables, each of said side plates being rigidly attached to one of the movable components of said first and second jacking means and extending below the alignment of said tension cables;

cross bar means connecting said side plates for rigidly maintaining said side plates in said parallel planes; and key means attached to said side plates at a vertical location adjacent said aligned cables for mating into corresponding receiving passages on the fastening heads to prevent rotary motion of said heads. 5. The apparatus of claim 3 further comprising: four guide rods connected to corresponding corners of said back plates -outside of said walls and fixed to said back plates to prevent axial motion of said rods;

first and second locking blocks, each slidably engaging two of said guide rods and extending out of said frame for engagement with said concrete surfaces, and

means carried by said rods for securing said l-ocking blocks thereto at a predetermined axial position.

6. The apparatus of claim 5 wherein said guide rails are each further defined by a plate elongated longitudinally of said cables attached at either end to said back plates and including an upper lip portion exten-ding to each side of the plane of said elongated plate and a lower lip portion extending only inwardly of the plane of sai-d elongated plate thereby defining a J-shaped cross section, and wherein said guide plate means are adapted to fit within the inner contour of said guide rails and constrained thereby from lateral movement, said first and second locking blocks being located respectively adjacent the outer surfaces of said elongated plates and below the upper lip portions thereof.

7. Apparatus for applying tensional force to first and second tension cables embedded in concrete for prestressing the same, each of said cables terminating in a fastening head extending out of facing surfaces of said concrete comprising:

`an elongated frame including first and second back plates extending in a plane transverse of said cables, and first and second side walls extending in parallel planes longitudinally of said cables and each fastened to said fir-st and second back plates, said side walls being further defined by elongated upper lip portions extending to either side of the plane of said walls and elongated lower lip portions extending only inwardly of said walls;

a first hydraulic cylinder and piston rod unit defining a fixed component attache-d to said rst back plate and a movable component;

a second hydraulic cylinder and piston rod unit dellining a fixed component attached to said sec-ond back plate and a movable component;

first guide plate means attached to the movable component of said first unit for engaging the inner contours of said frame side walls and constrained from lateral movement thereby t-o guide said movable component of said first unit in linear motion longitudinal of said first cable;

second guide plate means attached to the movable component of said second unit for engaging the inner contours of said frame side walls and constrained from lateral movement thereby to guide said movable component of said second unit in linear motion longit-udinal of said second cable and opposing the motion 'of said first unit;

first shoe means attached to the movable component of said first unit for engaging the fastening head of said fir-st cable to apply tension to said first cable when said first unit is expanded;

second shoe means attached to the movable component of `said second unit for engaging the fastening head lof said second unit to apply tension t-o said second cable when said second unit is expanded;

-rst and second guide rods connected to said first and second back plates and lying longitudinal of and exterior to said first frame side wall;

a first l-ocking block slidably carried by said first and second guide rods extending -outside of the space defined by said frame for engaging one of said .facing concrete surfaces;

first means threadably attached to said. first and second guide rods for securing said first. l-ocking block at a predetermined axial position;

third and fourth guide rods connected to said first and second back plates and lying longitudinal of and eX- terior to said second frame side wall;

a second locking block slidably carried by said third and fourth guide rods extending outside of the space defined by said frame for engaging one of said facing concrete surfaces; and

second means threadably attached to said first and second guide rods for securing said first locking block at a predetermined axial position..

y8. The apparatus of claim 7 wherein said first and second shoe means each include first and second elongated side plates extending below and on either side of said cables, and a key on each of said side plates for mating into a receiving portion on said fastening heads thereby preventing rotary motion of said heads.

9. Apparatus for use in applying tension force to first and second tension cables embedded in concrete for prestressing the same, each of .said cables coupled to a fastenying head and extending out of vertical, facing surface of said concrete, said concrete further defining a generally horizontal surface intersecting with upper edges of said facing, vertical surfaces, comprising: a rigid frame adapted for resting on said horizontal conc-rete surface; first and second hydraulic jacking means each having a first component mounted to said frame and a second component linearly moveable with respect to said first component longitudinally of said cable and including means for engaging said cable fastening heads; and means for selectively, independently actuating said liirst and second jacking means for moving said engaging means relative to each other thereby forcing said cable fastening heads relative to each other and applying tension to said cables.

10. The apparatus of clai-m 9 further comprising: block means slidable longitudinally of said frame for engaging one of said vertical side walls; and means for locking said block means to said frame against said wall, whereby tension in one of said cables may be selectively increased while tension in the other cable is maintained constant.

References Cited UNITED STATES PATENTS 2,696,040 12/1'954 Crom `et al. 29-452 3,089,215 5/1963 Stubbs 52-223 X 3,249,374 5/1966 Muche et al 52-223 X 3,285,569 11/1966 La Marr et al 254-29 MILTON S. MEHR, Primary Examiner'. 

